 
   These handlers take two arguments;  `db` and `event`, and they return `db`.
 
-  (fn [db event]
-     ....)
+      (fn [db event]
+         ....)
 
   So, the interceptor wraps the given handler:
      1. extracts two `:coeffects` keys: db and event

  can be slow. So, you won't want this interceptor present in production
  code. So condition it out like this :

    (re-frame.core/reg-event-db
       :evt-id
       [(when ^boolean goog.DEBUG re-frame.core/debug)]  ;; <-- conditional
       (fn [db v]
         ...))

  To make this code fragment work, you'll also have to set goog.DEBUG to
  false in your production builds - look in `project.clj` of /examples/todomvc.


  These handlers take two arguments;  `coeffects` and `event`, and they return `effects`.

      (fn [coeffects event]
         {:db ...
          :dispatch ...})

   Wrap handler in an interceptor so it can be added to (the RHS) of a chain:
     1. extracts `:coeffects`
